It will be recalled that galvanometers comprise pivoting elements provided with a winding pivotingly carried in the airgap of a magnet. A return spring biasses the elements towards a rest position. When a control current is applied to the winding, the resultant electromagnetic motor couple displaces the pivoting elements. The equilibrium position is obtained when the return couple defined by the spring equals the electromagnetic motor couple.
Logometers comprise pivoting elements provided with a magnet pivotally carried between two crossed windings receiving electric control currents. The movable magnet of the elements aligns itself with the magnetic field generated by the windings.